Gas fed water-heater

ABSTRACT

A gas fed water-heater has a double wall container ( 1 ) inside of which are arranged a burner ( 2 ) and a tank ( 3 ) of the water to be heated. At least in the portion ( 5 ′) adjacent to the burner ( 2 ) of the interspace ( 5 ) between the two walls of the container ( 1 ), a thermoinsulating system is placed comprising an inner layer ( 6 ) of glass wool or rock wool and an outer layer ( 7 ) formed of at least one vacuum panel, which is formed by an envelope which encloses inert material powder having an average particle size of less than 100 nanometers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/IT03/00350, filed Jun. 4, 2003, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a gas fed water-heater, particularly to a gas fed water-heater provided with a thermoinsulating system placed around the area of the burner to avoid heat losses.

It is known that water-heaters, usually referred to as “heaters”, can be fed by gas or electricity. The gas fed water-heaters of accumulation type comprise a generally cylindrical or parallelepiped container in which a gas burner and a tank containing the water to be heated are placed. The burner generally occupies the lower part of the container and is connected above to a heat exchanger traversing the tank, thus heating the water contained therein.

The container is generally formed with a double wall and an insulating material is arranged in the interspace enclosed by the double wall. This is necessary to avoid heat losses, which obviously would lower the energy yield of the water-heater. Usually, a polymeric insulator, for example a polyurethane foam, is inserted, particularly in the portion of the interspace adjacent to the tank, while in the portion adjacent to the position of the burner, glass wool or rock wool is used as insulating material.

However, this type of insulation has the drawback that to ensure a good thermal tightness in the burner area, which has a very high temperature (capable of reaching 250-300° C.), it is necessary to use a very thick layer of rock wool, thus increasing the total size of the water-heater or decreasing its capacity.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide a water-heater with a thermoinsulating system capable of efficiently avoiding heat loss, without increasing the volume of the insulator with respect to the systems utilized up to now. The object is achieved with a water-heater containing a thermoinsulating system in the interspace between the double walls of the container, wherein the thermoinsulating system comprises, at least in a first portion of the interspace adjacent to the burner, an inner layer of rock wool or glass wool and an outer layer formed of at least one vacuum panel, the vacuum panel comprising an envelope which encloses an inert material powder having an average particle size of less than 100 nanometers.

It has been found that, by placing a two layer thermoinsulating system according to the present invention, at least in the portion of the interspace of a water-heater which is adjacent to the burner, it is possible to improve the insulation of the water-heater, thus obtaining a power saving of about 10%.

Particularly, the best energy yield of the water-heater is achieved when the inner layer based on rock wool or glass wool occupies about 70-80% of the volume available for the thermoinsulating system, the remainder volume being occupied by the vacuum panel.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings an embodiment which is presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:

FIG. 1 is a longitudinal sectional view of a water-heater according to on embodiment of the invention; and

FIG. 2 is a cross sectional view of the water-heater along line II-II′ of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is shown a gas fed water-heater according to the present invention comprising in a known way a double wall container 1, cylindrically shaped, inside which are located a burner 2 and above it a tank 3 of the water to be heated. Burner 2 is connected above to a heat exchanger 4 traversing the tank 3, thereby heating the water contained therein. The double wall defines an interspace 5, whose lower portion 5′ is adjacent to the area occupied by the burner, while the upper portion 5″ is adjacent to the area of the tank. The dotted line of the drawing represents the separation between the two portions 5′ and 5″.

FIG. 2 represents a cross section of the water-heater perpendicular to the axis thereof at the height of portion 5′. As shown in FIG. 2, a thermoinsulating system is inserted in the lower area of the interspace, the system comprising at least two different layers, that is, an inner layer 6, nearer to burner 2, formed of rock wool or glass wool, and an outer layer 7 formed of at least one vacuum thermoinsulating panel.

The panel, comprising plastic materials, could not be placed in direct contact with the wall delimiting the burner, which reaches temperatures higher than 250° C. However, layer 6 has thermal insulating properties, so that the surface of this layer opposed to the one in contact with the burner is at a lower temperature, which the panel can withstand. In turn, the panel wrapped around layer 6 has higher thermal insulation properties than a layer of glass wool or rock wool of same thickness of the panel would have. By wrapping the panel around layer 6, a synergistic effect is thus obtained, with the inner layer protecting the panel from thermal deterioration, and the panel noticeably increasing the thermal insulation of the system with the same overall thickness.

The two layer thermoinsulating system could be present even in the portion 5″ of the interspace. However, since temperatures in this area are lower and do not require insulation of very high efficiency, it is preferable (even for economic reasons) to fill the portion 5″ with any known thermoinsulating material, for example a foamed polymeric material. The separation between the portions 5′ and 5″ of the interspace may be solely geometric, or may be obtained by a separation element.

As is known, a vacuum thermoinsulating panel is made up of an envelope in which a filling material is present under vacuum. The envelope has the function of preventing (or reducing as much as possible) the ingress of atmospheric gases into the panel, so as to keep a vacuum level compatible with the thermoinsulating level required from the application. The envelope is made with so-called “barrier” sheets, characterized by a gas permeability as low as possible. The filling material has the main function of spacing apart the two opposite faces of the envelope when vacuum is created in the panel. The filling must have a porous or discontinuous internal structure, so that the pores or interstices thereof can be evacuated to perform the thermoinsulating function.

The vacuum panel used in the water-heater according to the present invention comprises, as a filling material, an inert material powder having an average particle size of less than 100 nanometers, and preferably between 2 and 20 nanometers. As is known, the thermoinsulating properties of this type of panel vary only slightly as a function of the internal pressure, which can reach some tens of millibars without compromising these properties. For this reason, the envelope of these panels can advantageously be made of a plastic material, for example a polyolefin, possibly metallized.

According to a preferred embodiment of the invention, the inert material of the powder is silica, preferably mixed with mineral fibers, such as glass fibers, so as to be easily compressed to form boards having a thickness up to some millimeters, which can be bent relatively easily.

The silica used for the invention can be, for example, precipitated silica, manufactured for example by the German company Degussa GmbH. Preferably, pyrogenic silica is used, a form of silica obtained by burning SiCl₄ with oxygen in a suitable chamber, manufactured and sold for example by the U.S. company Cabot Corp. under the trademark Nanogel® or by the German company Wacker GmbH.

Possible changes and/or additions may be made by those skilled in the art to the embodiment of the invention here described and illustrated without departing from the scope of the same invention. 

1. A gas fed water-heater comprising a double wall container (1) inside of which are arranged a burner (2) and a tank (3) for water to be heated, the double wall defining an interspace (5) containing a thermoinsulating system, wherein the thermoinsulating system comprises, at least in a first portion (5′) of the interspace adjacent to the burner, an inner layer (6) of rock wool or glass wool and an outer layer (7) formed of at least one vacuum panel comprising an envelope which encloses an inert material powder having an average particle size of less than 100 nanometers.
 2. The water-heater according to claim 1, wherein the inner layer (6) has a volume percentage comprising between 70-80% of the total volume of the thermoinsulating system.
 3. The water-heater according to claim 1, wherein the inner layer of rock wool or glass wool and the at least one vacuum panel of the thermoinsulating system occupy only the first portion (5′) of the interspace adjacent to the burner (2).
 4. The water-heater according to claim 3, wherein a second portion (5″) of the interspace adjacent to the tank (3) is filled with a foamed polymeric material.
 5. The water-heater according to claim 1, wherein the inert material powder comprises particles with an average size between 2 and 20 nanometers.
 6. The water-heater according to claim 1, wherein the envelope comprises a plastic material.
 7. The water-heater according to claim 6, wherein the plastic material is metallized.
 8. The water-heater according to claim 1, wherein the inert material powder is mixed with mineral fibers.
 9. The water-heater according to claim 8, wherein the mineral fibers comprise glass fibers.
 10. The water-heater according to claim 1, wherein the inert material comprises pyrogenic silica. 